The STOP Act 2.0 aims to strengthen efforts against illicit substances, particularly opioids, entering the United States through international mail. It significantly increases the criminal penalty for mail fraud when a person knowingly misrepresents the country of origin of an international mail shipment, adding potential imprisonment of up to five years and fines, along with seizure and forfeiture authority for the Department of Homeland Security, thereby targeting deceptive practices that obscure the source of illegal goods. A crucial aspect of the bill is the termination of the authority to exclude countries from the requirement to transmit advance electronic information for 100 percent of mail shipments, with this exclusion authority ending five years after the bill's enactment. To ensure accountability and transparency, the bill mandates enhanced annual reports from the Secretary of Homeland Security on compliance with these advance electronic data requirements. These reports must detail agreements with foreign postal operators, assess data quality, summarize randomized test results, and list countries previously excluded from the 100% data requirement, including reasons for continued exclusion and steps taken towards compliance. Furthermore, the legislation promotes proactive measures to intercept illicit substances. It authorizes public-private partnerships to develop technology and processes for identifying the origin of fentanyl, other synthetic opioids, and their precursors. The bill also enables international collaboration and information sharing with allied foreign governments regarding problematic shippers and best detection practices, while requiring specialized training for U.S. Customs and Border Protection officers on detecting these dangerous substances. Finally, the Comptroller General is tasked with evaluating the implementation of the original STOP Act of 2018, identifying risks and assessing compliance differences between USPS and private carriers.